Cigarette smoking and cardiac output.

Although the hmmodynamic responses to cigarette smoking have been extensively studied, considerable controversy still exists as to the presence or degree of deleterious effects on the circulatory system (Roth and Shick, 1958). There is, however, general agreement that nicotine is the pharmacologically active substance in tobacco smoke (Comroe, 1960; Haag, 1940; Roth, 1960). From 1 to 4 mg. of nicotine is absorbed into the blood stream during the smoking of one cigarette when the smoke is inhaled (Pierce, 1941). Excitation of the adrenal medulla and peripheral sympathetic ganglia occurs with a resultant tachycardia and a rise of the circulating epinephrine level followed by stimulation of the supra-optic nuclei with the subsequent release of posterior pituitary hormone causing mild pressor effects (Burn, 1960). It has been postulated that either a constriction of coronary arteries or an increase in the work load of the heart beyond the ability of the coronary vessels to supply the myocardium with essential metabolic demands occurs as a result of cigarette smoking. "Tobacco angina" has been reported by Moschcowitz (1928), electrocardiographic changes by Russek, Zohman, and Dorset (1955), and changes in the ballistocardiogram by Thomas, Bateman, and Lindberg (1956). Bellet et al. (1962), using coronary sinus catheterization in dogs, reported an increase in the cardiac output and the coronary artery blood flow after intravenous nicotine, which was less in those animals in which coronary artery narrowing had been artificially created. This is in agreement with the work of Bargeron et al. (1957) who found an increased coronary blood flow and decreased coronary vascular resistance in normal men during cigarette smoking. It is possible that the acute effects of smoking may aggravate heart disease but there is as yet no basis on which to incriminate smoking in the pathogenesis of coronary or other types of heart disease. Bruce and Shillingford (1962) have recently developed a dye dilution technique for recording serial changes in cardiac output: we have used this technique to study the effects of cigarette smoking and intravenous nicotine on the cardiac output to determine the changes, if any, that occur.